Beam parameter product (BPP) control by varying fiber-to-fiber angle

ABSTRACT

An apparatus includes a laser system that includes a first fiber having an output end and situated to propagate a first laser beam with a first beam parameter product (bpp) and a second fiber having an input end spliced to the output end of the first fiber at a fiber splice so as to receive the first laser beam and to form a second laser beam having a second bpp that is greater than the first bpp, wherein the output end of the first fiber and the input end of the second fiber are spliced at a tilt angle so as to increase the first bpp to the second bpp.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 15/276,589 that was filed Sep. 26, 2016, which claims thebenefit of U.S. Provisional Patent Application No. 62/232,379 that wasfiled Sep. 24, 2015 and is related to U.S. Provisional PatentApplication No. 62/190,047 that was filed Jul. 8, 2015. Theseapplications are incorporated herein by reference in their entireties.

FIELD

The disclosure pertains to optical fiber laser systems and beam deliverysystems.

BACKGROUND

In meeting customer requirements and market demand, fiber laser systemsare often characterized by a set of output characteristics variable fromsystem to system, including output power and beam quality. For example,in some laser applications, perfect, diffraction-limited (or close toperfect) beam quality is necessary while in others a reduced beamquality is sufficient (or may even be preferred) to meet processrequirements. In addition, various steps of the laser process supplychain can benefit from having predictable beam quality. Also, indesigning fiber laser systems, it can be desirable to have sets ofcomponents that can be common across platforms and architectures. Whilemethods for maximizing laser beam quality have received much attention,low cost methods of manufacturing laser systems with selectable beamquality are lacking. Therefore, a need remains for solutions to overcomethese drawbacks.

SUMMARY

According to an aspect of the disclosed technology, an apparatusincludes a laser system that includes a first fiber having an output endand situated to propagate a first laser beam with a first beam parameterproduct (bpp) and a second fiber having an input end spliced to theoutput end of the first fiber at a fiber splice so as to receive thefirst laser beam and to form a second laser beam having a second bppthat is greater than the first bpp, wherein the output end of the firstfiber and the input end of the second fiber are spliced at a tilt angleso as to increase the first bpp to the second bpp.

According to another aspect of the disclosed technology, a methodincludes selecting a beam parameter product (bpp) increase associatedwith laser beam propagation from a first fiber to a second fiber,selecting a tilt angle between the first fiber and the second fiberbased on the selected bpp increase, and coupling the first fiber to thesecond fiber at the selected tilt angle.

According to another aspect of the disclosed technology, an apparatusincludes a fiber fixture situated to receive and secure an output end ofa first fiber in a first position and a second fiber in a secondposition, a fiber tip alignment mechanism situated to align the inputend of the first fiber proximate the output end of the second fiber, anda splicing mechanism situated to splice the aligned input end and outputend so as to form a fiber splice having a tilt angle corresponding to aselected beam parameter product (bpp) increase associated with beampropagation through the fiber splice from the first fiber to the secondfiber.

According to a further aspect of the disclosed technology, a methodincludes selecting a beam parameter product (bpp) increase associatedwith a laser beam propagation from a first fiber to a second fiber,positioning at least one of the first fiber and the second fiber so thata longitudinal axis of the corresponding first fiber or second fiber isoffset from a longitudinal axis of the other of the first fiber andsecond fiber or from a splice position between the first fiber andsecond fiber, wherein the offset is associated with the selected bppincrease, and splicing the first fiber and the second fiber together.

The foregoing and other objects, features, and advantages of thedisclosed technology will become more apparent from the followingdetailed description, which proceeds with reference to the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view schematic of a fiber splicing apparatusembodiment.

FIG. 2 is a schematic of an example laser system.

FIG. 3 is a perspective view of an example fusion splicing apparatus.

FIG. 4 is a graph of beam parameter product with respect to tilt angle.

FIG. 5 is a table of beam parameter values related to the graph in FIG.4 .

FIG. 6A illustrates an intensity profile associated with a zero anglesplice.

FIG. 6B illustrates an intensity profile associated with a non-zeroangle splice.

FIG. 7 is another graph of beam parameter product with respect to tiltangle.

FIG. 8 is a table of values related to the graph in FIG. 7 .

FIG. 9A illustrates an intensity profile associated with a zero anglesplice.

FIG. 9B illustrates an intensity profile associated with a non-zeroangle splice.

FIG. 10 is a graph of bpp as a function of tilt angle.

FIG. 11 illustrates an intensity profile for a beam transmitted througha splice with a non-zero tilt angle.

FIG. 12 illustrates an intensity profile of a beam that has propagatedthrough a zero angle splice.

FIG. 13 illustrates an intensity profile of a beam that has propagatedthrough a non-zero angle splice.

FIG. 14 is a graph of bpp with respect to tilt angle for several splicesamples.

FIGS. 15 and 16 are flowcharts of example splicing methods.

FIGS. 17A-17B are side view schematics of an example splicing apparatus.

FIG. 18 shows an end view cross-section of an example fiber fixture.

FIGS. 19-21 shows examples of a sets of fibers arranged in position tobe spliced.

DETAILED DESCRIPTION

As used in this application and in the claims, the singular forms “a,”“an,” and “the” include the plural forms unless the context clearlydictates otherwise. Additionally, the term “includes” means “comprises.”Further, the term “coupled” does not exclude the presence ofintermediate elements between the coupled items.

The systems, apparatus, and methods described herein should not beconstrued as limiting in any way. Instead, the present disclosure isdirected toward all novel and non-obvious features and aspects of thevarious disclosed embodiments, alone and in various combinations andsub-combinations with one another. The disclosed systems, methods, andapparatus are not limited to any specific aspect or feature orcombinations thereof, nor do the disclosed systems, methods, andapparatus require that any one or more specific advantages be present orproblems be solved. Any theories of operation are to facilitateexplanation, but the disclosed systems, methods, and apparatus are notlimited to such theories of operation.

Although the operations of some of the disclosed methods are describedin a particular, sequential order for convenient presentation, it shouldbe understood that this manner of description encompasses rearrangement,unless a particular ordering is required by specific language set forthbelow. For example, operations described sequentially may in some casesbe rearranged or performed concurrently. Moreover, for the sake ofsimplicity, the attached figures may not show the various ways in whichthe disclosed systems, methods, and apparatus can be used in conjunctionwith other systems, methods, and apparatus. Additionally, thedescription sometimes uses terms like “produce” and “provide” todescribe the disclosed methods. These terms are high-level abstractionsof the actual operations that are performed. The actual operations thatcorrespond to these terms will vary depending on the particularimplementation and are readily discernible by one of ordinary skill inthe art.

In some examples, values, procedures, or apparatus' are referred to as“lowest”, “best”, “minimum,” or the like. It will be appreciated thatsuch descriptions are intended to indicate that a selection among manyused functional alternatives can be made, and such selections need notbe better, smaller, or otherwise preferable to other selections.Examples are described with reference to directions indicated as“above,” “below,” “upper,” “lower,” and the like. These terms are usedfor convenient description, but do not imply any particular spatialorientation.

As used herein, optical radiation refers to electromagnetic radiation atwavelengths of between about 100 nm and 10 μm, and typically betweenabout 500 nm and 2 μm. Examples based on available laser diode sourcesand optical fibers generally are associated with wavelengths of betweenabout 800 nm and 1700 nm. In some examples, propagating opticalradiation is referred to as one or more beams having diameters,asymmetric fast and slow axes, beam cross-sectional areas, and beamdivergences that can depend on beam wavelength and the optical systemsused for beam shaping. For convenience, optical radiation is referred toas light in some examples, and need not be at visible wavelengths.

Representative embodiments are described with reference to opticalfibers, but other types of optical waveguides can be used having square,rectangular, polygonal, oval, elliptical or other cross-sections.Optical fibers are typically formed of silica (glass) that is doped (orundoped) so as to provide predetermined refractive indices or refractiveindex differences. In some, examples, fibers or other waveguides aremade of other materials such as fluorozirconates, fluoroaluminates,fluoride or phosphate glasses, chalcogenide glasses, or crystallinematerials such as sapphire, depending on wavelengths of interest.Refractive indices of silica and fluoride glasses are typically about1.5, but refractive indices of other materials such as chalcogenides canbe 3 or more. In still other examples, optical fibers can be formed inpart of plastics. In typical examples, a doped waveguide core such as afiber core provides optical gain in response to pumping, and core andcladdings are approximately concentric. In other examples, one or moreof the core and claddings are decentered, and in some examples, core andcladding orientation and/or displacement vary along a waveguide length.

As used herein, numerical aperture (NA) refers to a largest angle ofincidence with respect to a propagation axis defined by an opticalwaveguide for which propagating optical radiation is substantiallyconfined. In optical fibers, fiber cores and fiber claddings can haveassociated NAs, typically defined by refractive index differencesbetween a core and cladding layer, or adjacent cladding layers,respectively. While optical radiation propagating at such NAs isgenerally well confined, associated electromagnetic fields such asevanescent fields typically extend into an adjacent cladding layer. Insome examples, a core NA is associated with a core/inner claddingrefractive index, and a cladding NA is associated with an innercladding/outer cladding refractive index difference. For an opticalfiber having a core refractive index n_(core) and a cladding indexn_(clad), a fiber core NA is NA=√{square root over (n_(core) ²−n_(clad)²)}. For an optical fiber with an inner core and an outer core adjacentthe inner core, a cladding NA is NA=√{square root over (n_(inner)²−n_(outer) ²)}, wherein n_(inner) and n_(outer) are refractive indicesof the inner cladding and the outer cladding, respectively. Opticalbeams as discussed above can also be referred to as having a beam NAwhich is associated with a beam angular radius. While multi-core stepindex fibers are described below, gradient index designs can also beused. Some examples include fibers that support a few modes, and can bereferred to as “few mode” fibers. Such fibers have a normalizedfrequency parameter (V-number) defined as V=2·π·a·NA/λ wherein λ isvacuum wavelength, ‘a’ is a fiber core radius, and NA is numericalaperture. For large V-number, a total number ‘t’ of modes ‘M’ supportedby a fiber is approximately M=4·V²/π²+2. For single-mode fibers, V isless than about 2.405. As used herein, a few mode fiber is defined as afiber for which a V-number is less than about 5, 10, or 20.

In some examples disclosed herein, a waveguide core such as an opticalfiber core can be doped with a rare earth element such as Nd, Yb, Ho,Er, or other active dopants or combinations thereof. Such actively dopedcores can provide optical gain in response to optical or other pumping.As disclosed below, waveguides having such active dopants can be used toform optical amplifiers, or, if provided with suitable optical feedbacksuch as reflective layers, mirrors, Bragg gratings, or other feedbackmechanisms, such waveguides can generate laser emissions. Optical pumpradiation can be arranged to co-propagate and/or counter-propagate inthe waveguide with respect to a propagation direction of an emittedlaser beam or an amplified beam. In further examples, a waveguide corecan be doped with one or more passive dopants, such as Ge, P, Al, Fl,and B so as to increase, decrease, or maintain a refractive index.

A laser beam parameter product (bpp) is generally equal to the productof the radius of the laser beam waist and the half angle of the laserbeam's divergence. The ratio of a bpp of a laser beam to the bpp of acorresponding ideal Gaussian beam provides an M² beam quality value forcomparing different beams. Exemplary laser beams typically containmultiple transverse optical modes. Such multimode (or few mode) beamstypically have M² values greater than about 2, whereas single-mode beamstypically have M² values less than about 2. In some examples, thesingle-mode beams and multimode beams have M² value of less than orgreater than about 1.8, 1.6, 1.5, 1.4, or lower, respectively. Intypical examples, a multimode beam has at least a significant portion ofthe power content of the multimode beam in one or more transverseoptical modes higher than a fundamental LP₀₁ mode. Beam radii are oftenmeasured from a center to position where the beam has a 1/e² value ofthe peak intensity of the beam, though other normalizing or averagingoptions may be used. Divergence angles are typically determined in thefar field, such as several Rayleigh lengths from a beam focus.

Fusion splicers typically include opposite fiber fixtures situated tosecure opposing ends of fibers to be spliced. The opposing ends of thefibers are arranged in a center region that includes a fusion splicingmechanism, such as pair of electrodes between which the opposing fiberends are situated for fusing and across which an arc is generated toproduce the heat for the fusion splicing. Other fusion splicers caninclude laser sources to generate heat for fusion splicing the opposingfiber ends, or a chemical source, such as a gas flame. After the fiberfixtures secure the opposing fiber ends in the center region, a fusioncover of the fusion splicing mechanism is lowered over the secured fiberends. A z-axis movement stage can bring one or both of the fibers inproximity to each other for fusion splicing and an x-y-z movement stagecan bring one or both of the fiber tips situated in proximity so thatcores, claddings, or other reference surfaces of the opposing fiber tipsare aligned before heat is applied by the fusion splicer.

In FIG. 1 , an apparatus 100 includes a first fiber 102 with a firstfiber end 104 and a second fiber 106 with a second fiber end 108 eachsituated in a fusion splicer fixture 110 so that the first and secondfiber ends 104, 108 are in proximity to each other. In particular, thefirst and second fiber ends 104, 108 are situated at a tilt angle θinstead of being parallel to each other. By situating the first andsecond fiber ends 104, 108 at the tilt angle θ and fusion splicingtogether the first and second fiber ends 104, 108, the beam parameterproduct of a beam propagating from the first fiber 102 to the secondfiber 104 through the splice increases by an amount associated with theangle θ. In typical examples, the amount of bpp increase increases asthe tilt angle increases. In representative embodiments, the bppincrease occurs as the beam passes through the splice.

The fusion splicing fixture 110 includes fiber supports 112, 114 andclamping mechanisms 116, 118 for the first and second fibers 102, 106,respectively. The clamping mechanisms 116, 118 typically come in varioussizes associated with the diameter or other characteristic of the fiberto be inserted into the fusion splicer fixture 110. As shown, the firstand second fibers 102, 106 have equal outer diameters of 500 μm. Thesecond clamping mechanism 118 is sized for 500 μm fibers so that thesecond fiber 106 extends generally horizontally over fiber support 114.The first clamping mechanism 116 is sized for 350 μm fibers so that thefirst fiber 102 extends horizontally and at a tile angle due to theposition of the fiber support 112 and the mismatch between the firstclamping mechanism 116 and the diameter of the first fiber 102. As shownin FIG. 1 , the first and second fibers 102, 106 each include respectivecores 120, 122 and claddings 124, 126 with the diameter of the core 120of the first fiber 102 being considerably smaller than the core 122 ofthe second fiber 106. Thus, in the example shown, the first fiber 102 isa fiber laser fiber situated to propagate a fiber laser beam rangingfrom about 100 W to multiple kW and the second fiber 106 is a multimodedelivery fiber situated to receive the beam and deliver the beam to atarget for various applications, such as cutting, welding, etc.

FIG. 3 shows an image of a fusion splicer fixture 300 with a first fiber302 having a 510 μm outer diameter being secured in an outer fusionsplicer fixture 304 having a V-groove associated with a 350 μm fiber.The first fiber 302 extends through an inner fusion splicer fixture 306having a V-groove for receiving the fiber. The inner fusion splicerfixture 306 is generally laterally translatable so as to position theend of the first fiber 302 in alignment a second fiber end and with apair of electrodes 308, 310 that extend perpendicular to a longitudinaldirection of the first fiber 302 and are situated to provide energy forfusion splicing of the first fiber to a second fiber (not shown).Suitable fusion splicers are commercially available from Fitel andFujikura. However, arranging fibers, such as the first fiber 302 and thesecond fiber, at selectable tilt angles is generally not supported asconventional splicers seek to avoid any tilt between adjacent fiber endsto be spliced. Various other methods may be used, in view of the presentdisclosure, to provide the tilt angle, including translation stagesadjusting relative heights and angles of fiber sections to be spliced,as well as fusion splicers suitably programmed and having suitable fiberend to fiber end adjustment mechanisms. Furthermore, one or both fiberends of the first fiber 302 and second fiber to be spliced can also becleaved at a selected non-zero angle perpendicular to the longitudinalfiber axes of the corresponding fiber ends.

FIG. 2 shows an apparatus 200 including a laser source 202, a claddinglight stripper 204, and a delivery fiber 206. The laser source 202 caninclude one or more gain fibers, such as a fiber oscillator or a fiberoscillator with one or more fiber amplifiers, as well as other types oflaser sources that can provide an optical beam. The laser source 202 iscoupled to the cladding light stripper 204 directly or with a passivefiber section 208. The cladding light stripper 204 is coupled directlyor with a passive fiber section 210 to the delivery fiber 206. At one ormore locations between the laser source 202 and a fiber laser beamoutput 212, a fiber splice optically couples adjacent fiber sections sothat a beam generated by the laser source 202 propagates through theoptical fiber splice and increases the beam parameter product of thegenerated beam by a selected, or close to a selected, amount associatedwith the fiber laser beam output 212. The selected increase in beamparameter product is caused by a non-zero angle between fiber-splicedadjacent fiber sections. As the beam generated by the laser source 202propagates through the splice, the non-zero angle causes the beam tofill additional transverse modes in the downstream fiber section.Suitable locations for the beam parameter product increasing opticalfiber splice include one or more of the cladding light stripper 204,delivery fiber 206, and connecting passive sections 208, 210. In someexamples, the beam parameter product increasing optical fiber splice canbe situated before or between fiber gain sections, such as before afiber oscillator or before a fiber amplifier, or after a finaloscillator or amplifier fiber. The increase in bpp can be associatedwith the improved filling of modes of a downstream gain fiber.

FIG. 4 is a chart showing simulation results predicting the increase inbeam parameter product for a single-mode beam propagating through a 14μm diameter core propagating through a fiber splice with respectivefiber sections tilted at an angle during the splice. From a baselinebeam parameter product of about 0.95 mm-mrad, the beam parameter productincreases smoothly with increasing tilt angle. FIG. 5 is a tablecorresponding to the chart in FIG. 4 showing predicted increases invarious beam features as tilt angle associated with the fiber splice isincreased. In general, relatively small angles, ranging from about 0.5degrees to 5 degrees achieve suitable ranges of increase in beamparameter product. FIG. 6A shows the intensity profile of a resultingoutput beam after a corresponding input beam has propagated through afiber splice, where the fiber sections that were spliced were arrangedend to end at a zero angle. FIG. 6B shows the intensity profile of aresulting output beam after a corresponding input beam has propagatedthrough a fiber splice, where the fiber sections that were spliced werearranged at an angle of 1.0 degrees.

FIG. 7 is a chart showing simulation results predicting the increase inbeam parameter product for a multimode beam propagating in a 40 μmdiameter core and propagating through a fiber splice with respectivefiber sections tilted at an angle during the splice. A baseline beamparameter product of about 2.0 mm-mrad steadily increases at the tiltangle associated with the spliced fiber ends increases. FIG. 8 is atable corresponding to the chart in FIG. 7 showing predicted increasesin various beam features along perpendicular x and y axes perpendicularto the direction of propagation, including spot size Wx, Wy, beamquality Mx2, My2, beam parameter product BPPx, BPPy, BPPr (an average ofx and y), as tilt angle increases. FIG. 9A shows the intensity profileof a resulting output beam after a corresponding input beam haspropagated through a fiber splice, where the fiber sections that werespliced were arranged end to end at a zero angle. FIG. 9B shows theintensity profile of a resulting output beam after a corresponding inputbeam has propagated through a fiber splice, where the fiber sectionsthat were spliced were arranged at an angle of 1.0 degrees.

FIG. 10 shows simulated data of beam parameter product as a function oftilt angle along with experimental results associated with fiber splicesat 0.0 degrees and 0.7 degrees. FIG. 11 shows simulated and experimentalresults for the intensity profile of the multi-kW beams associated withthe beam parameter product results in FIG. 10 for the fiber splicehaving 0.7 degree tilt angle. FIG. 12 shows beam output results for a0.0 degree fiber splice tilt angle (i.e., no tilt) and FIG. 13 showsbeam output results for a 0.7 degree fiber splice tilt angle. As shownin the side graphs 1302, 1304 corresponding to the intensity profilesacross perpendicular axes of the beam, a flat middle portion with smallcenter depression is established with the increased tilt angle. Thus,the mode field distribution of the beam propagating in the receivingfiber of a spliced fiber pair changes from Gaussian (or another initialdistribution) to other shapes, such as flat-top, ring-shaped, or anothershape, based on the increase in splice tilt angle.

FIG. 14 shows a graph 1400 depicting the relationship between bppincrease and tilt angle for several samples of splices of fibers withequal 500 μm outer diameters that were spliced with the same Fitelfusion splicer. In a first group of samples 1402, a fusion splicer clampfixture having a v-groove designed to receive a 500 μm fiber is used forthe first fiber and for the second fiber. The corresponding splicesamples show a very low angle between the two fibers of about 0.2° orless, showing effectively a zero tilt angle between first and secondfibers. In general, the tilt angle between the fibers was very low,typically 0.2° degrees or less, which is similar to the angle toleranceachieved in conventional splices. In a second group of samples 1404, a500 μm fusion splicer clamp fixture having a v-groove designed toreceive 500 μm fiber was used for one fiber in each splice and a 350 μmfusion splicer clamp fixture having a v-groove designed to receive a 350μm fiber was used for the other fiber in each splice. For example,v-groove depth, width, cross-section, can be adjusted to correspond tofibers of different diameters. The corresponding results show thepresence of a tilt angle, ranging from about 0.6° to 1.2°, between thelongitudinal axes of the spliced fibers after fusion splicing. Theincrease in angle can be attributed to a longitudinal axis offsetbetween the second fiber and the first fiber (or splicer electrodes)provided by the 350 μm fusion splicer clamp fixture. A third group ofsamples 1406 includes splices formed by positioning both 500 μm fibersin undersized 350 μm fusion splicer clamp fixtures. Both fibers becameoffset in relation to the splicer electrodes so that during alignment ofthe fibers and prior to the splice, the fiber tips were angled towardsthe electrodes. The resulting splice includes a range of tilt anglesthat were concentrated between about 1.5° to 2.0°.

FIG. 15 shows an example method 1500 for increasing a beam bpp by aselected amount or into a range of bpp increases. At 1502, a bppincrease amount is selected for a beam that propagates from a firstfiber to a second fiber. At 1504, a tilt angle between the first fiberand the second is selected that is based on the selected bpp increase.In typical examples, tilt angles can correspond to an angle betweenlongitudinal axes or end faces of the first and second fibers. At 1506,the end faces of the first and second fibers are coupled, for example,with a fusion splice, so as to form the tilt angle selected at 1504 andto produce a bpp increase for the beam that corresponds to the bppincrease selected at 1502. Tilt angles are typically selected in therange of 0.2° to 5°, and more typically from about 0.5° to about 1.5°.In FIG. 16 , a method 1600 is shown that includes, at 1602, selected abpp increase that is associated with a laser beam propagating from afirst fiber to a second fiber. At 1604, one of the first and secondfibers is positioned so that a longitudinal axis of the respective fiberis provided with an offset from one or both of a longitudinal axis ofthe other fiber and a splice position where the ends of the first andsecond fibers are to be spliced. At 1606, the first and second fibersare spliced together. In representative examples, the offset provides atilt angle between the longitudinal axes of the first and second fibersduring the splicing at 1606.

FIGS. 17A-17B show an example fusion splicing apparatus 1700 that canproduce fiber splices with selectable bpp increases. The fusion splicingapparatus 1700 generally includes an outer fiber fixture portion 1702having a fiber receiving portion 1704 situated to receive a first fiber1706 with a predetermined fiber geometry and an outer fiber fixtureportion 1708 having a fiber receiving portion 1710 situated to receive asecond fiber 1712 with a predetermined fiber geometry. For example, thepredetermined fiber geometry associated with outer fiber fixtureportions 1702, 1708 can be a fiber cross-sectional area or outerdiameter. As shown, the cross-sectional area of the first fiber 1706 isthe same as that of the second fiber 1712. Typical fiber cross-sectionalareas can be associated with cladding diameters of 60 μm, 80 μm, 100 μm,200 μm, 350 μm, 500 μm, 660 μm, or smaller or larger or havingintermediate values in some examples. Fiber cross-sectional areas canalso be defined with respect to a core, inner cladding, outer cladding,buffer jacketing, or other fiber layers. Fiber cores can range fromsingle mode, to few-mode, to multimode, including 6 μm, 10 μm, 15 μm, 25μm, 50 μm, 100 μm, and 220 μm, or larger core diameters in someexamples.

The fiber receiving portion 1704 of the outer fiber fixture portion 1702is matched to the cross-sectional area or outer diameter of the firstfiber 1706 so that a longitudinal axis 1714 of the first fiber 1706secured in the outer fiber fixture portion 1702 is aligned with asplicer energy source 1716, such as an electrode, of a fiber splicermechanism 1718. The longitudinal axis 1714 typically corresponds to acenter axis of a fiber core 1720 that can be offset with respect to acladding but is more typically centrally positioned in the fibercross-section. The fiber receiving portion 1710 of the outer fiberfixture portion 1708 is not matched to the outer cladding diameter ofthe second fiber 1712 so that a longitudinal axis 1722 of the secondfiber 1712, typically centered about a fiber core 1724, becomes shiftedby an offset H above the longitudinal axis 1714 and the splicer energysource 1716 with the second fiber 1712 secured in the outer fiberfixture portion 1708. In some examples, the height offset H can beproduced by selecting the outer fiber fixture portion 1708 to correspondto a fiber cross-sectional area or outer diameter that is smaller thanthe cross-sectional area or outer diameter of the second fiber 1712. Infurther examples, a translation stage can be used to move the secondfiber 1712 or the outer fiber fixture portion 1708 to produce the heightoffset H. It will be appreciated that the term is used for convenienceand other designations, and the offset can be associated with a length,width, distance, dimension, shift, etc.

With additional reference to FIG. 17B, z-axis translation stages 1726,1728 are coupled to the outer fiber fixture portions 1702, 1708 so thatan end 1730 of the first fiber 1706 and an end 1732 of the second fiber1712 can be moved proximate each other. In some examples, the ends arebrought in contact, partial contact, or within 1/10, ¼, ½, or one coreradius of one of the cores 1720, 1724 and generally centered in relationto the splicer energy source 1716. Proximity and alignment precision canbe in the range of under a 1 μm to several μm. A fiber tip alignmentmechanism can include an X, Y, or XY translatable inner fiber fixtureportions 1734 a, 1734 b that are coupled to the ends 1730, 1732 andsituated proximate the splicer energy source 1716 so that the fibercores 1720, 1724 can be moved in relation to the other and brought inalignment. An alignment assistance mechanism 1736 a, 1736 b can assistwith the alignment of the fiber ends 1730, 1732 by coupling light intoone or both of the first fiber 1706 and the second fiber 1712 anddetecting an amount of light received by the receiving fiber. Thealignment assistance mechanism 1736 a, 1736 b can also include one ormore cameras allowing a magnified view of the fiber ends 1730, 1732. Thealignment assistance mechanism can be automated or manually controlledwith a splice control 1738. The splice control 1738 and a power source1740 are coupled to the fiber splicer mechanism 1718 so as to provideenergy for the splicer energy source 1716 and to control the splicecharacteristics of the splice produced with the fiber ends 1730, 1732.Because the longitudinal axis 1722 is provided with the offset H, thefiber ends 1730, 1732 are aligned with the inner fiber fixture portions1734 a, 1734 b so that the longitudinal axes 1714, 1722 form a tiltangle θ at the fiber ends 1730, 1732. The inner fiber fixture portions1734 can include spring loaded v-grooves in which the fiber ends 1730,1732 can be inserted and secured. With the fiber end 1732 secured asshown in FIG. 17B with the inner fiber fixture portion 1734 b urging thefiber end 1732 downward, the offset H and the distance between the innerand outer fiber fixture portions 1708, 1734 b can determine the amountof tilt in the tilt angle θ. A tilt angle, such as the tilt angle θ, canbe provided for the first fiber 1706 so as to combine with the tiltangle θ for the second fiber 1712 to produce a corresponding splice tiltof 2θ.

The tilt angle θ can be selected by varying the offset H or the distancebetween one or both of the outer fiber fixture portions 1702, 1708, theinner fiber fixture portions 1734 a, 1734 b, and the splice location ofthe fiber ends 1730, 1732, or both the offset H and the distance ordistances. In one example, both of the longitudinal axes 1714, 1722 areraised so as to be offset from the splice location. The fiber tipalignment mechanism then repositions the ends 1730, 1732 so that aresulting splice has an increased tilt angle θ. The bpp of a beam thatpropagates from the first fiber 1706 to the second fiber 1712 isincreased by an amount that corresponds to the selected tilt angle θ orthe selected offset H. For example, where a first bpp of a beam thatpropagates through an untilted splice increases to a second bpp, thefirst bpp of the beam after propagating through a tilted spliceincreases to a third bpp greater than the second bpp. Alternatively,where a first bpp of a beam that propagates through an untilted spliceremains the same, after propagation through the tilted splice, the firstbpp increases to a second bpp. As tilt angle θ increases, fiber splicescan become more susceptible to break, burn, or other failure, though insome examples, splice samples with tilt angles of greater than 0.2° andless than 1.5° did not produce a significant percentage of failures withpropagating beams with continuous powers of 800 W to 4 kW. The firstfiber 1706 and the second fiber 1712 can have various core and claddingdiameters. In some examples, for beams propagating from the first fiberto the second fiber, the diameter of the core 1724 is typically largerthan or the same size as the core 1720. Cladding diameters can vary, andin some examples, an outer cladding diameter of the first fiber 1706 canbe larger than, the same size, or smaller than the outer claddingdiameter of the second fiber 1712. In some examples, the increase in bppdoes not occur immediately at the splice but instead at a distance, suchas several cm, downstream from the splice.

FIG. 18 shows a side cross-section of a fiber fixture 1800 that includestop and bottom portions 1802, 1804 including a v-groove 1806 in thebottom portion 1804. A fiber 1808 associated with the dimensions of thev-groove 1806 is situated in the v-groove 1806 so that a center positionof a fiber core 1810 is situated at a reference plane 1812. With adifferent fiber 1814 that has an outer diameter that is oversized forthe v-groove 1806, a fiber core 1816 of the different fiber 1814 iselevated so as to be positioned at a reference plane 1818 spaced apartfrom the reference plane 1812. In some examples, V-groove geometry isvaried for different fixtures to correspond to fibers with differentouter diameters or to correspond with positioning a reference axis ofthe fiber 1808 at different reference planes. In further examples,V-groove geometry can remain fixed and fixture thickness can be variedfor different outer diameters or to provide a fiber with differentoffsets. For example, the bottom portion 1804 can have a largerthickness to correspond to a fiber with a smaller outer diameter or toreposition a fiber reference axis at a higher reference plane, such asreference plane 1818. In different examples, V-groove geometry, such asdepth, width, V-slope, curved or linear sides, etc. can be varied. Thus,in some examples, custom fixtures can be fabricated to provide differentoffsets for fibers to be spliced. In additional embodiments, a movementstage is coupled to the fixture, such as the bottom portion 1804 of thefiber fixture 1800, to raise, lower, provide lateral movement, or fiberrotation.

FIG. 19 shows an example fiber arrangement 1900 of a first fiber 1902and a second fiber 1904 secured in respective fiber fixtures 1906, 1908.The first fiber 1902 includes an angle-cleaved end 1910 tilted withrespect to a core axis 1912 of the first fiber 1902 by an angle 90−θ.The core axis 1912 of the first fiber 1902 is aligned so as to becollinear with a core axis 1914 of the second fiber 1904. Theangle-cleaved end 1910 is brought proximate a cleaved end 1916 of thesecond fiber 1904 that extends perpendicularly with respect to the coreaxis 1914. A splicing mechanism 1918, such as a pair of electrodes, issituated to fusion splice the angle-cleaved end 1910 and the cleaved end1916 together so as to form a splice that produces a bpp increase for abeam propagating from one of the fibers to the other one of the fibersbased on the tilt angle θ. In some examples, both the first fiber 1902and the second fiber 1904 can have angle-cleaved ends, and thelongitudinal axes 1912, 1914 can be rotated relative to each other todefine a tilt angle at the splice that varies based on the rotation.

In FIG. 20 , a first fiber 2002 is secured in a fiber fixture 2004 thatis situates an angle-cleaved end 2006 of the first fiber 2002 and a coreaxis 2008 of the first fiber 2002 in a splice position adjacent asplicing mechanism 2010. The angle-cleaved end 2006 is at an angle θ₁with respect to a plane perpendicular to the core axis 2008. A secondfiber 2012 is secured in a corresponding fiber fixture 2014 so that acore axis 2016 of the second fiber 2012 extends at a tilt angle θ2 withrespect to the core axis 2008 and approximately intersects the core axis2008 of the first fiber 2002 at the angled-cleaved end 2006. The tiltangle θ2 can be the same as the angle θ₁ so that the angle-cleaved end2006 is parallel and proximate a cleaved end 2018 of the second fiber2012 at the splice position.

FIG. 21 shows another example splice arrangement 2100 of a first fiber2102 and a second fiber 2104 secured in respective fixtures 2106, 2108so that respective longitudinal axes 2110, 2112 are angled at a tiltangle θ and intersect at a splice position of a splicer mechanism energysource 2114. The first fiber 2102 and second fiber 2104 includerespective cleaved ends 2116, 2118 that are perpendicular to therespective longitudinal axes 2110, 2112. A fusion splice joining thecleaved ends 2116, 2118 provides a tilt angle between the first fiber2102 and the second fiber 2104 that produces an increase in a bpp for abeam propagating from one of the fibers to the other one of the fibers.

Having described and illustrated the principles of the disclosedtechnology with reference to the illustrated embodiments, it will berecognized that the illustrated embodiments can be modified inarrangement and detail without departing from such principles. Forinstance, elements of the illustrated embodiments, such as splice tiltangle control, tilt angle and bpp selection, etc., can be implemented insoftware or in hardware of a fusion splicing apparatus or a controlleror computer coupled to the fusion splicing apparatus. Also, thetechnologies from any example can be combined with the technologiesdescribed in any one or more of the other examples. It will beappreciated that procedures and functions such as those described withreference to the illustrated examples can be implemented in a singlehardware or software module, or separate modules can be provided. Theparticular arrangements above are provided for convenient illustration,and other arrangements can be used.

In view of the many possible embodiments to which the principles of thedisclosed technology may be applied, it should be recognized that theillustrated embodiments are only representative examples and should notbe taken as limiting the scope of the disclosure. Alternativesspecifically addressed in these sections are merely exemplary and do notconstitute all possible alternatives to the embodiments describedherein. For instance, various components of systems described herein maybe combined in function and use. We therefore claim all that comeswithin the scope and spirit of the appended claims.

We claim:
 1. An apparatus, comprising: a fiber fixture situated toreceive and secure an output end of a first fiber in a first positionand a second fiber in a second position; a fiber tip alignment mechanismsituated to align an input end of the first fiber proximate an outputend of the second fiber, the fiber tip alignment mechanism comprising afirst inner fiber fixture portion and a second inner fiber fixtureportion, the first and second inner fiber fixture portions beingtranslatable in one or more directions; and a splicing mechanismsituated to splice the aligned input end and output end so as to form afiber splice having a selected tilt angle corresponding to a selectedbeam parameter product (bpp) increase associated with beam propagationthrough the fiber splice from the first fiber to the second fiber. 2.The apparatus of claim 1, wherein the splicing mechanism is a fusionsplicing mechanism.
 3. The apparatus of claim 1, wherein the firstposition and second position correspond to an offset between one or moreof a longitudinal axis of the first fiber, a longitudinal axis of thesecond fiber, and a splice position associated with the splicingmechanism.
 4. The apparatus of claim 1, wherein the selected tilt anglecorresponds to an angle between a longitudinal axis of the first fiberat the splice and a longitudinal axis of the second fiber at the splice.5. The apparatus of claim 1, wherein the selected tilt angle correspondsto a first angle between an output surface at the output end of thefirst fiber and a plane perpendicular to a longitudinal axis of thefirst fiber at the output end, a second angle between an input surfaceat the input end of the second fiber and a plane perpendicular to alongitudinal axis of the second fiber at the input end, or a combinationof the first angle and the second angle, at the aligned input and outputends.
 6. The apparatus of claim 1, wherein the fiber fixture comprises afirst outer fiber fixture portion configured to receive and secure theoutput end of the first fiber and a second outer fiber fixture portionconfigured to receive and secure a first end of the second fiber.
 7. Theapparatus of claim 6, wherein the first outer fiber fixture has alongitudinal axis extending through the first outer fiber fixture thatis offset by a selected height from a longitudinal axis extendingthrough the second outer fiber fixture.
 8. An apparatus, comprising: afiber fixture situated to receive and secure an output end of a firstfiber in a first position and a second fiber in a second position, thefiber fixture comprising a first outer fiber fixture portion configuredto receive and secure the output end of the first fiber and a secondouter fiber fixture portion configured to receive and secure a first endof the second fiber; a fiber tip alignment mechanism situated to alignan input end of the first fiber proximate an output end of the secondfiber; a splicing mechanism situated to splice the aligned input end andoutput end so as to form a fiber splice having a selected tilt anglecorresponding to a selected beam parameter product (bpp) increaseassociated with beam propagation through the fiber splice from the firstfiber to the second fiber; and a translation stage configured to movethe second outer fiber fixture relative to the first outer fiber fixtureto create a selected height offset between a longitudinal axis extendingthrough the second outer fiber fixture and a longitudinal axis extendingthrough the first outer fiber fixture.
 9. The apparatus of claim 8,wherein the translation stage is a first translation stage and whereinthe apparatus further comprises one or more additional translationstages configured to move the first and second fibers toward and awayfrom one another.
 10. The apparatus of claim 1, wherein the first andsecond inner fiber fixture portions are translatable along a first axisand a second axis perpendicular to the first axis.
 11. The apparatus ofclaim 1, wherein the first and second inner fiber fixture portions eachcomprise a spring loaded v-groove.
 12. The apparatus of claim 1, whereinthe fiber tip alignment mechanism further comprises one or more camerasconfigured to provide a magnified view of the first and second fibers.13. A splicing apparatus for coupling a first optical fiber having afirst longitudinal axis to a second optical fiber having a secondlongitudinal axis, comprising: a first fiber fixture portion configuredto secure a first end portion of the first optical fiber such that thefirst longitudinal axis is disposed at a first height; a second fiberfixture portion configured to secure a first end portion of the secondoptical fiber such that the second longitudinal axis is disposed at asecond height; a translation stage coupled to at least one of the firstfiber fixture portion and the second fiber fixture portion, thetranslation stage being configured to move the first end portion of thefirst optical fiber relative to the first end portion of the secondoptical fiber thereby permitting selection of a tilt angle between thefirst longitudinal axis and the second longitudinal axis prior tosplicing the first end portion of the first optical fiber to the firstend portion of the second optical fiber; and a fiber tip alignmentmechanism including a first inner fiber fixture portion configured tosecure an output end of the first optical fiber and a second inner fiberfixture portion configured to secure an input end of the second opticalfiber, the first and second inner fiber fixture portions beingtranslatable along a first axis and along a second axis perpendicular tothe first axis.
 14. The splicing apparatus of claim 13, wherein thefirst height is offset from the second height by a selected heightoffset.
 15. The splicing apparatus of claim 13, wherein the translationstage is a first translation stage and wherein the splicing apparatusfurther comprises one or more additional translation stages coupled toat least one of the first and second fiber fixture portions, the one ormore additional translation stages being configured to move the firstand second fibers toward and away from one another.
 16. The splicingapparatus of claim 13, wherein the first and second inner fiber fixtureportions each comprise a spring loaded v-groove.
 17. The splicingapparatus of claim 13, wherein the fiber tip alignment mechanism furthercomprises one or more cameras configured to provide a magnified view ofthe output end of the first optical fiber and the input end of thesecond optical fiber.
 18. The splicing apparatus of claim 13, whereinthe first and second inner fiber fixture portions are translatable alongthe first axis toward and away from the first and second fiber fixtureportions respectively, and wherein the distance between the inner fiberfixture portions and the fiber fixture portions determines the selectedtilt angle.
 19. The apparatus of claim 6, further comprising atranslation stage configured to move the second outer fiber fixturerelative to the first outer fiber fixture to create a selected heightoffset between a longitudinal axis extending through the second outerfiber fixture and a longitudinal axis extending through the first outerfiber fixture.
 20. The apparatus of claim 19, wherein the translationstage is a first translation stage and wherein the apparatus furthercomprises one or more additional translation stages configured to movethe first and second fibers toward and away from one another.